Recent insights into the plant ARP2/3 complex

More than two decades have passed since the first identification of the ARP2/3 complex in plants. During this time, numerous studies have advanced our understanding of the complex's role in actin cytoskeleton regulation. However, compared with opisthokonts, the mechanisms and functional contexts of ARP2/3 activity in plants remain only partially understood. Since the last comprehensive synthesis, substantial progress has been made in elucidating plant-specific features of ARP2/3 regulation, including upstream control via the WAVE/SCAR module, emerging roles of additional nucleation-promoting factors, and evidence for subunit specialization. This review shows that plant ARP2/3 acts as a context-dependent, membrane-associated actin nucleator instead of a global organizer of the cortical actin network. We summarize current knowledge on the localized activities of ARP2/3 at distinct membrane systems-including the plasma membrane, endomembranes, and autophagy-related structures-and discuss the mechanisms that recruit ARP2/3 to these membranes and enable its functions in cell expansion, membrane trafficking, immunity, and symbiotic interactions. Despite this progress, the downstream mechanistic consequences of ARP2/3-nucleated branched actin in plants remain largely unresolved.